Every last drop: Putting limited data to use in understanding multiple impacts of hydrologic alteration on native fish communities in the Big Bend region of the Rio

Authors: Grande. Brian G . Laub1, Phaedra Budy2, 1

Year: 2016 (xlviii)

Abstract

Hydrologic alteration impacts patterns of floods and droughts, water quality, physical habitat characteristics, and can provide favorable conditions for nonnative species. Understanding the relative importance of these different and often synergistic factors for native fish communities is critical for prescribing river management actions. However, data for conducting such analysis is often limited, particularly in desert rivers lacking charismatic, endangered sport fishes that garner significant money and attention. The Big Bend reach of the Rio Grande is a case in point, because although the area is critically important for Rio Grande native fish, and even with land protected on both sides of the river, there are no charismatic native fishes that attract the attention of public and private agencies to the degree, for example, of Pacific salmon. Thus, we are challenged with using limited data to identify the most important factors for native fish can help prioritize future studies and management effort. Toward this end, we synthesize current understanding of the river ecosystem in a conceptual model emphasizing links between physical, e.g., habitat and water quality, and biotic components, e.g., fish and invertebrate communities. We analyzed existing data on fish communities, active channel width, hydrology, and water quality at several sites using structural equation models, in order to gain insight into the relative importance of different controlling factors on the fish community. The model results suggest active channel width, nonnative fish relative abundance, and hydrologic forcing all have strong direct effects on the native fish community, and hydrologic forcing has strong indirect effects on native species richness through water quality and nonnative relative abundance. The models also reveal that primary limiting factors differ for different fish species. For example, water quality had a much stronger influence on red shiner than on speckled chub, which was more strongly correlated with c hannel width. Although data limitations warrant some caution in interpretation, the models reveal important hypotheses to test in future research and provide a method for using limited data collection efforts to better understand multiple, interacting fact ors driving native fish communities.